Cocoa: Fix 'first responder' error on macOS 10.12

Error message is displayed during the startup because Cocoa view is set
as the first responder for window but this view isn't in this window
(actually it is not in any window at all).

Fixes #876.
Closes #883.

src/cocoa_window.m

@@ -1032,11 +1032,11 @@ static GLFWbool createNativeWindow(_GLFWwindow* window,
     [window->ns.view setWantsBestResolutionOpenGLSurface:YES];
 #endif /*_GLFW_USE_RETINA*/
 
+    [window->ns.object setContentView:window->ns.view];
     [window->ns.object makeFirstResponder:window->ns.view];
     [window->ns.object setTitle:[NSString stringWithUTF8String:wndconfig->title]];
     [window->ns.object setDelegate:window->ns.delegate];
     [window->ns.object setAcceptsMouseMovedEvents:YES];
-    [window->ns.object setContentView:window->ns.view];
     [window->ns.object setRestorable:NO];
 
     return GLFW_TRUE;